The present invention relates to conveyor, and to a workpiece carrier for a conveyor.
A conveyor is made known in DE 40 36 214 C2. According to FIG. 1 in DE 40 36 214 C2, the conveyor includes a workpiece carrier 4 which is driven in a frictional manner via drive means designed as conveyor rollers 3 or conveyor belts, in which case the drive means define a plane of conveyance. Furthermore, an inner guide and an outer guide are provided, which guide the workpiece carrier in a laterally sliding manner and thereby define a conveyor track for it, and in which case the conveyor track describes a curve. The outer guide is formed by a first and a second straight outer guide section 5 which are oriented perpendicularly to one another, and which are interconnected via a concavely curved outer guide section 7 such that the workpiece carrier is guided without interruption. The curved outer guide section is formed by a separate guide piece 7 which is fastened to the straight outer guide sections.
The inner guide is situated equidistantly to the outer guide at a specified track width, thereby resulting in a first and a second straight inner guide section 5 which are interconnected via a curved inner guide section 6a. The circularly curved inner guide section is situated tangentially to the straight inner guide sections, thereby ensuring smooth guidance of the workpiece carrier on the inner guide as well. The track width is selected to be minimally greater than the width of the workpiece carrier, and so the workpiece carrier is designed to slide without play or friction.
The drive means and its driving force extend only parallel to the straight sections of the conveyance path, and so they do not extend parallel to the direction of conveyance in the region of the curve. This results in the problem that the driving force in the curve acts on the workpiece carrier at an unfavorable angle, while the tractive resistance in the curve is simultaneously increased relative to the straight-ahead travel of the workpiece carrier. To convey the plate-type workpiece carrier around the curve in the most reliable manner possible, its lateral side is designed to have a rounded oblong shape. However, due to the frictional driving action between the drive means and the conveyor, it is possible for the workpiece carrier to become stuck in the curve. The possibility that workpiece carriers may become stuck in the curve poses a serious problem, because conveyors of this type are typically part of a larger flow-line production system. If the conveyance flow becomes interrupted, the entire production line therefore quickly comes to a standstill, thereby possibly resulting in considerable production losses. It is therefore expected that the curve of a conveyor function in a highly reliable manner, and that it be nearly impossible for the workpiece carrier to become stuck.
The curve described in DE 40 36 214 C2 is characterized by the fact that the radius of curvature of the curved inner guide section is very small. As a result, the workpiece carrier performs an approximately purely rotational motion in the curve when it is engaged with the curved inner guide section in a guiding manner. Since the curved inner guide section is very short in the circumferential direction, the sliding motion is very slow when traveling around the curve, and the friction is therefore minimal. It is simultaneously ensured that the workpiece carrier remains favorably oriented relative to the drive means at all times when traveling around the curve. This curve shape is different, e.g., from the curve shape made known in FIG. 9 in U.S. Pat. No. 4,928,806, in which the curved inner guide has a much greater turning radius. In curves of this type, a separate drive is usually required in the curve region, since the workpiece carrier undergoes considerable displacement, in addition to pure rotation.
A consequence of the small turning radius of the curved inner guide described in DE 40 36 214 C2 is the likewise relatively small turning radius of the curved outer guide, which results in a high frictional force between the outer guide and the workpiece carrier. In addition, the rounded oblong shape of the workpiece carrier usually results in there being a great deal of unused space which may not be utilized by the workpieces, which is why a rectangular workpiece carrier is usually preferred.